Prince William tugs at heartstrings with touching tribute to Kate that no one noticed

Prince William made a touching tribute to Princess Kate as he attended the Ceremonial Welcome of Emperor Naruhito and Empress Masako of Japan on Tuesday.

The guests are in the UK until Friday, and have a number of events planned during the week.

During the welcome ceremony at Horse Guards Parade, there was a moment where the Emperor, Empress, King Charles, Queen Camilla, and Prince William were all standing on a stage.

But William left a gap between himself and the other royals in what appeared to be an acknowledgment of Kate's absence.

Kate is still undergoing preventative treatment after she announced she was diagnosed with cancer earlier this year.

The Princess of Wales made a brief return to public engagements on June 15 as she attended Trooping the Colour, but it is still not known when she might return to full-time royal duties.

READ MORE: William and Kate to make major change behind the scenes

In a written statement confirming her appearance at Trooping the Colour, Kate said: "I have been blown away by all the kind messages of support and encouragement over the last couple of months.

"It really has made the world of difference to William and me and has helped us both through some of the harder times.

"I am making good progress, but as anyone going through chemotherapy will know, there are good days and bad days.

"On those bad days you feel weak, tired and you have to give in to your body resting. But on the good days, when you feel stronger, you want to make the most of feeling well.

"My treatment is ongoing and will be for a few more months. On the days I feel well enough, it is a joy to engage with school life, spend personal time on the things that give me energy and positivity, as well as starting to do a little work from home.

"I’m looking forward to attending The King’s Birthday Parade this weekend with my family and hope to join a few public engagements over the summer, but equally knowing I am not out of the woods yet.

"I am learning how to be patient, especially with uncertainty. Taking each day as it comes, listening to my body, and allowing myself to take this much-needed time to heal.

"Thank you so much for your continued understanding, and to all of you who have so bravely shared your stories with me."

The royals were pictured last night at Buckingham Palace as they attended a state banquet for the Emperor and Empress of Japan.

It was an extravagant event, featuring gold cutlery and a menu comprised of poached Scottish langoustines and Cornish turbot.

Dessert was ice cream with a peach sorbet insert on compressed peaches.

In his speech, King Charles said: "Our governments are working together to provide a stable world for future generations.

"Supporting all these shared endeavours are the enduring ties between our people that transcend geography - and that does not just mean how much we enjoy tea and talking about the weather."

Emperor Naruhitio used his speech to pay tribute to the late Queen Elizabeth II.